It’s a reference to a scene from the ping pong animation, where one of the characters (Kong Wenge) sings ‘Hitori Bocchi no Christmas Eve’. You can see here at 1:02 https://youtu.be/8i93vXUKqnI?si=B0JyPaPttL5HXSrA
Yoshida-san, why art thou so cruel? Give us the best, most reliable friends we could count on, and force us to assassinate the last one. Why? Is it a lesson on how cruel the universe is to take all our friends away? Or a comment on the necessary strength to keep going forward without using the diary or new game+ to revive old cherished moments?